This invention relates broadly to grounding terminals and more particularly to terminal assemblies adapted for creating a grounding path from a grounding shield layer in a multiconductor communication cable.
Multiconductor cables are widely used to convey communication and various low strength signals and must be carefully shielded, usually by a metallic shield layer as part of a multilayer cable construction. The outer layer of such a cable is usually of an elastomeric wear-resistant material of a given thickness. The shield is usually directly beneath the elastomeric coating and is typically of a relatively thin, highly conductive material, such as aluminum. Frequently, the innermost surface of the shield is coated with a very thin layer of nonconductive material to avoid any potential contact with the conductors contained therein. It is the existence of the insulative layers both on the outer and inner surfaces of the shield that has created problems in effecting an efficient grounding path from the shield to an external grounding connection.
For example, one prior art proposal utilizes a stud with a shoe inserted in the cable so that the upper surface of the shoe is in contact with the inner surface of the shield. The stud extends outwardly of the cable either through an aperture formed in the outer insulative layer and shield or through a slit created longitudinally in the outer layers. A clamping plate and nut are inserted over the stud and clamping pressure applied to the system draws the shoe tightly up into engagement with the inner surface of the shield. The conductive path is then formed from the shoe through the stud to a secondary grounding strap which is connected and clamped to the stud. This system, however, also places the outer elastomeric material in compression and, with time, this elastomeric material will be subjected to cold flow causing the joint to relax and consequently causing the aggressive clamping pressure between the shoe and the sheath to diminish. Such a situation, obviously, creates an unreliable bounding path.
Improvements to such systems have been developed wherein a plurality of conductive paths are created in a system as generally described by placing a U-shaped, highly conductive strap between the shoe and the sheath at one end and between the upper pressure plate and a clamping nut at the other end. This, while producing a higher capacity connection, still does not overcome the cold flow problem presented by allowing the elastomeric sheath to become an active part in the clamping system.
Accordingly, it is a primary object of this invention to provide a grounding clamp assembly for use in shielded, multiconductor cables which produces a resilient clamping joint that does not include the elastomeric outer sheath as part of the active clamping system.
A further object of the invention is to provide an easily installed and handled clamping system which effects a grounding path from the conductive shield of a multiconductor cable to an outside grounding source.
An accompanying advantage of the invention is the creation of a grounding connector which will accommodate various relaxations in the clamping joint without harming the efficiency of the electrical connection.
A still further advantage of the present invention is the incorporation of a high-strength, mechanical clamping connector which provides a plurality of conductive paths from a shield in a multiconductor cable to a grounding strap.
The above and other objects and advantages are obtained by the three principal parts of the invention comprising a stud member having a radially extending flange, a preassembled nut and washer with insulation-piercing and spring take-up features and a prevailing torque or self-locking clamping nut adapted to clampingly secure a grounding strap to stud and preassembled nut and washer. The washer is preassembled to the nut in a conventional fashion but the washer itself is configured to provide a conical spring section at its inner periphery and a plurality of downwardly extending teeth members at its outer periphery. The teeth members preferably extend generally parallel to the axis of the washer and are adapted to pierce completely through the outer elastomeric sheath of a cable and into aggressive clamping connection with the upper surface of the shield. The teeth are also advantageously configured to that their free extremities include some means to limit the extent of penetration into the shield so as to not completely penetrate but only to embed into the upper surface. The flange of the stud is, preferably, arcuate in profile and has serrations formed on its upper surface to enhance the conductive contact between the lower or inner surface of the shield and the stud.
The invention may also include some configuration on the stud device, such as a polygonal head-like protrusion, within the arcuate, concave surface of the flange to prevent relative rotation between the stud and the cable during assembly. A modification of the preferred embodiment of the invention may be an asymmetrical arrangement of teeth about the periphery of the washer. This will aid in shipping and handling in that a mass of nut and washer assemblies will resist nesting or tangling with one another.